Level converter circuit

ABSTRACT

An embodiment level converter circuit is configured to receive, as a current supply, a current proportional to temperature.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of French Patent Application No. 2008274, filed on Aug. 4, 2020, which application is hereby incorporated herein by reference.

TECHNICAL FIELD

The present disclosure generally relates to electronic devices and circuits. The present disclosure more specifically applies to the forming of a circuit for converting levels of an analog signal.

BACKGROUND

An analog signal may be enabled to transmit binary information. For this purpose, the data are represented by the voltage level of the signal. The signal represents a logic “1” if the voltage is greater than a first voltage level: the high threshold, and represents a logic “0” if the voltage is smaller than a second voltage level: the low threshold.

A level converter circuit is a circuit used to offset the voltage levels, and thus the high and low thresholds, used by an analog signal to represent binary data.

It would be desirable to at least partly improve certain aspects of known level converter circuits.

SUMMARY

There is a need for higher-performance level converter circuits.

An embodiment overcomes all or part of the disadvantages of known converter circuits.

An embodiment provides a level converter circuit capable of receiving, as a current, a current proportional to temperature.

According to an embodiment, the circuit comprises a first inverter circuit comprising a first transistor of a first type and a second transistor of a second type.

According to an embodiment, the first and second transistors are MOS transistors.

According to an embodiment, the first transistor is an N-type MOS transistor and the second transistor is a P-type MOS transistor.

According to an embodiment, the second transistor is capable of receiving the current proportional to temperature on its gate.

According to an embodiment, the first transistor is capable of receiving an input signal on its gate.

According to an embodiment, the input signal has a variable high voltage level.

According to an embodiment, the input signal has a high voltage level randomly variable between two voltage levels.

According to an embodiment, the first and second transistors form part of a conversion circuit comprised within the level converter circuit.

According to an embodiment, the circuit comprises a current supply circuit capable of supplying the current proportional to temperature.

According to an embodiment, the conversion circuit and the supply circuit are formed on a same substrate.

According to an embodiment, the current supply circuit comprises a first current mirror circuit.

According to an embodiment, the first current mirror circuit comprises N-type MOS transistors.

According to an embodiment, the current supply circuit comprises a second current mirror circuit.

According to an embodiment, the second current mirror circuit comprises P-type MOS transistors.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features and advantages, as well as others, will be described in detail in the following description of specific embodiments given by way of illustration and not limitation with reference to the accompanying drawings, in which:

FIG. 1 very schematically shows in the form of blocks an embodiment of a level converter circuit;

FIG. 2 shows an example of implementation of the embodiment of FIG. 1;

FIG. 3 shows an equivalent diagram of the circuit of FIG. 2; and

FIG. 4 shows another equivalent diagram of the circuit of FIG. 2.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Like features have been designated by like references in the various figures. In particular, the structural and/or functional features that are common among the various embodiments may have the same references and may dispose identical structural, dimensional and material properties.

For the sake of clarity, only the steps and elements that are useful for an understanding of the embodiments described herein have been illustrated and described in detail.

Unless indicated otherwise, when reference is made to two elements connected together, this signifies a direct connection without any intermediate elements other than conductors, and when reference is made to two elements coupled together, this signifies that these two elements can be connected or they can be coupled via one or more other elements.

In the following disclosure, unless otherwise specified, when reference is made to absolute positional qualifiers, such as the terms “front”, “back”, “top”, “bottom”, “left”, “right”, etc., or to relative positional qualifiers, such as the terms “above”, “below”, “higher”, “lower”, etc., or to qualifiers of orientation, such as “horizontal”, “vertical”, etc., reference is made to the orientation shown in the figures.

Unless specified otherwise, the expressions “around”, “approximately”, “substantially” and “in the order of” signify within 10%, and preferably within 5%.

FIG. 1 schematically shows in the form of blocks an embodiment of a level converter circuit 10.

Converter circuit 10 receives, as an input, an analog input signal IN and outputs an analog output signal OUT. Input and output signals IN and OUT are used to transfer binary data. Converter circuit 10 is capable of converting the voltage levels of input signal IN into different voltage levels, output signal OUT corresponding to the converted input signal IN. The succession of logic states of output signal OUT is thus the same as that of input signal IN. More particularly, input signal IN is an analog signal comprising two states, a low state representing a logic “0” having a voltage level smaller than a first voltage level VinL, and a high state representing a logic “1” having a voltage level greater than a second voltage level VinH. Second voltage level VinH is greater than first voltage level VinL. Output signal OUT is an analog signal comprising two states, a low state representing a logic “0” having a voltage level smaller than a first voltage level VoutL, and a high state representing a logic “1” having a voltage level greater than a second voltage level VoutH. Second voltage level VoutH is greater than first voltage level VoutL.

Optionally, converter circuit 10 may output a second output signal N-OUT. Output signal N-OUT is an analog signal comprising two logic states, a low state representing a logic “0” having a voltage level smaller than voltage level VoutL, and a high state representing a logic “1” having a voltage level greater than voltage level VoutH. Output signal N-OUT represents a succession of logic states corresponding to the inverse of the logic states represented by output signal OUT.

Converter circuit 10 comprises a conversion circuit ii (LS) receiving input signal IN and outputting output signal OUT and, optionally, output signal N-OUT. The conversion circuit receives, as a current, a current Itemp and receives, as voltages, voltage levels VinL, VoutH, and VoutL. Converter circuit 10 does not receive voltage level VinH. A detailed example of conversion circuit 11 is described in relation with FIG. 2.

Converter circuit 10 further comprises a power supply circuit 12 (IPTAT) capable of supplying current Itemp. Current Itemp is a current proportional to the room temperature. An example of power supply circuit 12 is detailed in relation with FIG. 2.

According to an embodiment, conversion circuit 11 and power supply circuit 12 are both formed on a same substrate, for example, a same silicon substrate.

Converter circuit 10 operates as follows. When input voltage IN is greater than a threshold VIH, output voltage OUT is set to voltage level VoutH and output voltage N-OUT is set to voltage level VoutL. When input voltage IN is smaller than or equal to a threshold VIL, output voltage OUT is set to voltage level VoutL, and output voltage N-OUT is set to voltage level VoutH. Voltage levels VinL and VoutL are smaller than threshold VIL. Voltage levels VinH and VoutH are greater than threshold VIH.

The inventors have observed that by supplying conversion circuit ii with a current proportional to temperature, the number of conversion errors, that is, the number of erroneously converted bits, decreases. A conversion error may for example correspond to a non-compliance with a threshold VIH or VIL. Indeed, controlling an input transistor of conversion circuit ii with current Itemp proportional to temperature enables to compensate for the drift of the switching threshold of the transistor. This phenomenon will be detailed in relation with FIGS. 3 and 4.

In certain cases, the thresholds are defined by a standard, and an advantage of converter circuit 10 is that, due to the supply of its conversion circuit with the current proportional to temperature, it may comply with the standard.

Another advantage of converter circuit 10 is that it enables to convert input signal IN without knowing the “high” voltage level VinH. Thus, converter circuit 10 may convert an input signal IN having its “high” voltage level VinH varying, for example, randomly, between a plurality of voltage levels. According to an embodiment, the voltage level VinL of input signal IN is in the order of o V, the voltage level VinH of input signal IN varies randomly between a voltage in the order of 1.8 V, and a voltage in the order of 3.3 V.

FIG. 2 illustrates an electric diagram of an embodiment of the level converter circuit 10 described in relation with FIG. 1.

The conversion circuit 11 (delimited in dotted lines) of circuit 10 comprises a first inverter stage formed of MOS transistors 111N and 111P. Transistor 111N is of type N, and transistor 111P is of type P. Transistors 111N and 111P are coupled, preferably connected, in series by their conduction terminals. The source of transistor 111N is coupled, preferably connected, to a node receiving voltage level VinL. The drain of transistor 111N is coupled, preferably connected, to a node A. The gate of transistor 111N is coupled, preferably connected, to a node receiving input signal IN. The source of transistor 111P is coupled, preferably connected, to a node receiving voltage level VoutH. The drain of transistor 111P is coupled, preferably connected, to node A. The gate of transistor 111P is coupled, preferably connected, to a node receiving current Itemp. Further, transistor 111P is mirror-connected with transistors of power supply circuit 12, and is not used as a switch.

Conversion circuit 11 further comprises a second inverter stage formed of MOS transistors 112N and 112P. Transistor 112N is of type N and transistor 112P is of type P. transistors 112N and 112P are coupled, preferably connected, in series by their conduction terminals. The source of transistor 112N is coupled, preferably connected, to the node receiving voltage level VinL. The drain of transistor 112N is coupled, preferably connected, to a node B. The gate of transistor 112N is coupled, preferably connected, to node A. The source of transistor 112P is coupled, preferably connected, to the node receiving voltage level VoutH. The drain of transistor 112P is coupled, preferably connected, to node B. The gate of transistor 112P is coupled, preferably connected, to node A.

Conversion circuit 11 further comprises a third inverter stage formed of MOS transistors 113N and 113P. Transistor 113N is of type N and transistor 113P is of type P. Transistors 113N and 113P are coupled, preferably connected, in series by their conduction terminals. The source of transistor 113N is coupled, preferably connected, to a node receiving voltage level VoutL. The drain of transistor 113N is coupled, preferably connected, to a node C supplying output signal N-OUT. The gate of transistor 113N is coupled, preferably connected, to a node supplying output signal OUT. The source of transistor 113P is coupled, preferably connected, to the node receiving voltage level VoutH. The drain of transistor 113P is coupled, preferably connected, to node C. The gate of transistor 113 is coupled, preferably connected, to node B.

Conversion circuit 11 further comprises a fourth inverter stage formed of MOS transistors 114N and 114P. Transistor 114N is of type N, and transistor 114P is of type P. Transistors 114N and 114P are coupled, preferably connected, in series by their conduction terminals. The source of transistor 114N is coupled, preferably connected, to the node receiving voltage level VoutL. The drain of transistor 114N is coupled, preferably connected, to the node supplying output signal OUT. The gate of transistor 114N is coupled, preferably connected, to node C. The source of transistor 114P is coupled, preferably connected, to the node receiving voltage level VoutH. The drain of transistor 114P is coupled, preferably connected, to the node supplying output signal OUT. The gate of transistor 114P is coupled, preferably connected, to node A.

N-type MOS transistors 111N, 112N, 113N, and 114N are all sized to be conductive when the voltage at their gate is greater than threshold voltage VIH. P-type MOS transistors 111P, 112P, 113P, and 114P are all sized to be conductive when the voltage at their gate is greater than threshold voltage VIL.

The power supply circuit 12 (delimited in dotted lines) of circuit 10 comprises a first current mirror formed of two P-type MOS transistors 121P and 122P. The source of transistor 121P is coupled, preferably connected, to the node receiving voltage level VoutH. The drain of transistor 121P is coupled, preferably connected, to a node D. The gate of transistor 121P is coupled, preferably connected, to a node E. The source of transistor 122P is coupled, preferably connected, to the node receiving voltage level VoutH. The drain of transistor 122P is coupled, preferably connected, to node E. The gate of transistor 122P is coupled, preferably connected, to node E.

Power supply circuit 12 further comprises a second current mirror formed of two N-type MOS transistors 123N and 124N. The source of transistor 123N is coupled, preferably connected, to the node receiving voltage level VinL. The drain of transistor 123N is coupled, preferably connected, to node D. The gate of transistor 123N is coupled, preferably connected, to node D. The source of transistor 124N is coupled, preferably connected, to a first terminal of a resistor R. The second terminal of resistor R is coupled, preferably connected, to the node receiving voltage level VinL. The drain of transistor 124N is coupled, preferably connected, to node E. The gate of transistor 124N is coupled, preferably connected, to node D.

The transistors 121P, 122P, 123N, and 124N, of circuit 12, all operate in a low inversion mode. The current Itemp supplied by circuit 10 is then proportional to the ratio of the difference between the potentials present on the gate and the source of transistors 121P and 122P to the resistance of resistor R. The resistance of resistor R being inversely proportional to temperature, current Itemp is proportional to temperature.

The general operation of the embodiment of circuit 10, detailed in relation with FIG. 2, is described in relation with FIGS. 3 and 4.

FIG. 3 is a first equivalent electric diagram of the level converter circuit 10 described in relation with FIG. 2, in the case where input signal IN represents a logic “0”.

In FIG. 2, a so-called “conductive” transistor is represented by the electronic symbol of an on switch, and a so-called “non-conductive” transistor is represented by the electronic symbol of an off switch.

When input signal IN represents a logic “0”, its voltage is in the order of VinL, and is smaller than threshold VIL. Thus, the transistor 111N of conversion circuit 11 is non-conductive. The current control of transistor 111P is performed by current Itemp and the potential of node A is set to VoutH by transistor 111P.

Transistors 112N and 112P are controlled by the potential of node A. Transistor 112N is then conductive and transistor 112P is then non-conductive. Node B is coupled to the node receiving voltage level VinL.

Transistor 113P is controlled by the potential of node B and is then conductive. Node C is coupled to the node receiving voltage level VoutH. Output signal N-OUT then represents a logic “1” since its voltage is equal to voltage level VoutH.

Transistor 114P is controlled by the potential of node A and is then non-conductive. Transistor 114N is controlled by the potential of node C and is then conductive. The node supplying output signal OUT represents a logic “0” since its voltage is equal to voltage level VoutL.

Transistor 113N is controlled by output signal OUT and is then non-conductive. Node C is thus only coupled to the node receiving voltage level VoutH.

FIG. 4 is a first equivalent electric diagram of the level converter circuit 10 described in relation with FIG. 2, in the case where input signal IN represents a logic “1”.

In FIG. 4, a so-called “conductive” transistor is represented by the electronic symbol of an on switch and a so-called “non-conductive” transistor is represented by the electronic symbol of an off switch.

When input signal IN represents a logic “1”, its voltage is in the order of VinH, and is greater than threshold VIH. Thus, the transistor 111N of conversion circuit 11 is conductive. The current control of transistor 111P is performed by current Itemp and the potential of node A is set to VinL by transistor 111N.

Transistors 112N and 112P are controlled by the potential of node A. Transistor 112N is then non-conductive and transistor 112P is then conductive. Node B is coupled to the node receiving voltage level VoutH.

Transistor 113P is controlled by the potential of node B and is then non-conductive.

Transistor 114P is controlled by the potential of node A and is then conductive. The node supplying output signal OUT is coupled to the node receiving voltage VoutH. Output signal OUT represents a logic “1” since its voltage is equal to voltage level VoutH.

Transistor 113N is controlled by output signal OUT and is then conductive. Node C is thus coupled to the node receiving voltage level VoutL. Output signal N-OUT then represents a logic “0” since its voltage is equal to voltage level VoutH.

Transistor 114N is controlled by the potential of node C and is thus non-conductive.

Various embodiments and variants have been described. Those skilled in the art will understand that certain features of these various embodiments and variants may be combined, and other variants will occur to those skilled in the art. In particular, other embodiments of conversion circuits and of current power supply circuits supplying a current proportional to temperature may be envisaged.

Finally, the practical implementation of the described embodiments and variations is within the abilities of those skilled in the art based on the functional indications given hereabove. 

What is claimed is:
 1. A level converter circuit comprising: a first input configured to receive, as a current supply, a current proportional to a temperature.
 2. The level converter circuit according to claim 1, further comprising a first inverter circuit comprising a first transistor of a first type and a second transistor of a second type.
 3. The level converter circuit according to claim 2, wherein the first and second transistors are metal-oxide-semiconductor (MOS) transistors.
 4. The level converter circuit according to claim 3, wherein the first transistor is an N-type MOS transistor and the second transistor is a P-type MOS transistor.
 5. The level converter circuit according to claim 2, wherein a gate of the second transistor is configured to receive the current proportional to the temperature.
 6. The level converter circuit according to claim 2, wherein a gate of the first transistor is configured to receive an input signal.
 7. The level converter circuit according to claim 6, wherein the input signal is representative of a binary value and has a variable high voltage level.
 8. The level converter circuit according to claim 7, wherein the variable high voltage level is randomly variable between two voltage levels.
 9. The level converter circuit according to claim 2, wherein the first and second transistors are part of a conversion circuit within the level converter circuit.
 10. The level converter circuit according to claim 1, further comprising a current supply circuit configured to supply the current proportional to the temperature.
 11. The level converter circuit according to claim 10, further comprising: a first inverter circuit comprising a first transistor of a first type and a second transistor of a second type, wherein: the first and second transistors are part of a conversion circuit within the level converter circuit; and the conversion circuit and the current supply circuit are disposed on a same substrate.
 12. The level converter circuit according to claim 10, wherein the current supply circuit comprises a first current mirror circuit.
 13. The level converter circuit according to claim 12, wherein the first current mirror circuit comprises N-type MOS transistors.
 14. The level converter circuit according to claim 12, wherein the current supply circuit comprises a second current mirror circuit.
 15. The level converter circuit according to claim 14, wherein the second current mirror circuit comprises P-type MOS transistors.
 16. A level converter circuit comprising: a first input configured to receive, as a current supply, a current proportional to a temperature; and a first inverter circuit comprising a first transistor of a first type and a second transistor of a second type; wherein a gate of the second transistor is configured to receive the current proportional to the temperature; and wherein a gate of the first transistor is configured to receive an input signal.
 17. The level converter circuit according to claim 16, wherein the first transistor is an N-type metal-oxide-semiconductor (MOS) transistor and the second transistor is a P-type MOS transistor.
 18. The level converter circuit according to claim 16, further comprising a current supply circuit configured to supply the current proportional to the temperature.
 19. The level converter circuit according to claim 18, wherein: the first and second transistors are part of a conversion circuit within the level converter circuit; and the conversion circuit and the current supply circuit are disposed on a same substrate.
 20. The level converter circuit according to claim 18, wherein the current supply circuit comprises first and second current mirror circuits.
 21. A level converter circuit comprising: an analog input configured to receive an input signal varying between a low voltage level and a high voltage level, wherein the high voltage level is greater than the low voltage level; a conversion circuit configured to: receive a supply current proportional to temperature, without receiving the high voltage level as a supply voltage; and convert the input signal to an output signal; and a digital output configured to output the output signal. 